Since lead is harmful to human bodies, a lead-free solder alloy is going to be in widespread use. Sn is widely used as a basic composition because of the low melting point thereof and the relatively low production costs thereof Solder alloys that have been developed in view of this includes a tin-copper based solder alloy of eutectic Sn—Cu solder with Cu containing of about 0.7 weight percent added thereto, and a solder alloy resulting from adding Ag to the copper based solder alloy to ensure further intensity.
Technical advance improves electronic circuit architecture techniques of ICs and the like, and permits electronic devices to be downsized. Lead line spacing pitch of ICs becomes extremely narrow, and miniature design is required of a solder joint accordingly. For example, solder balls currently in widespread use have typically a diameter of 20 microns.